As is known in the art, power supplies for dc distribution systems, computers, telecommunications and data centers, as well as for transportation, lighting, displays, and medical applications among many other areas require high power density and fast response, provide electrical isolation and operate efficiently. In many cases, there is a desire for efficiency at high conversion ratios and/or over wide operating ranges (of voltages and/or powers). There is also a desire to achieve a high degree of integration, manufacturability and reliability. Traditionally, magnetic converter-based architectures with isolation transformers are widely used, such as forward converters, flyback converters and related architectures. Such architectures are simple, low-cost and easy to control. There is, however, a continued trend to operate power converters at ever increasing switching frequencies and as switching frequencies increase the converter timing required in the aforementioned architectures becomes difficult to satisfy, and the parasitic effects significantly increase the loss.
As is also known, circuits using high-gain transformers or coupled inductors is one approach to building converters in these applications. Circuits incorporating tapped inductors can provide desirable duty ratios and reduces device switching stress. However, the leakage inductance of such tapped inductors can ring with the parasitic capacitance of the switches, limiting its feasibility at high switching frequency. High-frequency-link architectures can reduce or eliminate this ringing problem by absorbing parasitics such as transformer leakage inductance into circuit operation. Such circuits can often also realize soft switching and switch at a higher frequency than conventional hard-switched architectures.
Nevertheless, as desired operating switching frequencies keep increasing, parasitic effects which are sometimes ignored, such as the proximity effect loss and transformer parasitic capacitances, can become very important. Furthermore, requirements that a system achieve high performance over wide operating range makes the system design even more challenging.